In recently years, a technique is practiced that involves molding a paste containing inorganic powder such as ceramic powder or glass powder dispersed in a binder resin composition, followed by burning to produce a fine molded product.
For example, a multilayer capacitor is generally produced through the following steps. First, after adding a plasticizer, a dispersing agent or the like to a solution of a binder resin dissolved in an organic solvent, ceramic material powder is added, and then the solution is homogenously mixed by a three-roll mill, beads mill, ball mill and the like mixing device. The resultant mixture is then defoamed to obtain a ceramic slurry composition in the form of a paste having a specific viscosity. The obtained slurry composition is then formed into a sheet form by making it flow and extend on a supporting surface of a polyethylene terephthalate film processed for mold release or of a stainless plate with the use of a coater such as doctor blade or reverse roll coater. After distilling off volatile solvents and the like, e.g., by heating, the molded product is released from the supporting member to obtain a ceramic green sheet.
Then on this ceramic green sheet, a conductive paste which is to form an internal electrode is applied by, for example, screen printing. A plurality of such ceramic green sheets on which the conductive paste is applied are alternately stacked and bonded by thermal compression to give a laminate. The conductive paste used in this case is mainly composed of a metal material such as palladium or nickel constituting an electrode, an organic solvent having compatibility to the surface of ceramic green sheet, and a binder resin such as ethyl cellulose.
Then after conducting a process of thermo-decomposing a binder component or the like contained in the laminate as a constituent of ceramic green sheet and conductive paste under heat and removing the same (so-called degreasing process), a ceramic burnt product is obtained by burning. Through a process of sintering an external electrode on an end face of the ceramic burnt product, a laminate ceramic capacitor is obtained.
For example, a plasma display (hereinafter, also referred to as PDP) has a basic structure made up of a pair of glass substrates which constitute a panel main body, a fluorescent layer, filler gas based on neon and/or xenon, a dielectric layer, a partition and an electrode. The electrode may be formed of a material such as Ag paste or Cu—Al alloy. The electrode may be obtained, for example, patterning after forming a metal film on a glass substrate by thick film printing or vapor deposition. There are known two types of PDPs: AC type which is driven by AC voltage or pulse voltage, and DC type which is driven by DC voltage. In an AC type PDP, an electrode is covered with a dielectric layer, and in a DC type PDP, an electrode is disposed to a discharge space. Also employed is a method in which a dielectric layer is formed by burning a binder resin composition in which low melting point glass is dispersed.
Further, in the DC type PDP, it is necessary to use a glass substrate having a partition. Conventionally, as a method of producing a glass substrate having a partition, a method in which a partition is formed by forming a pattern on a glass substrate with a paste of ceramic powder mixed with an organic binder, a solvent and the like by a thick film printing, followed by drying and burning (so-called thick film printing method, see Patent document 1, for example); and a method in which a partition is formed by printing a paste obtainable by mixing ceramic powder with an organic binder, solvent and the like, on a glass substrate in a flat manner at a predetermined film thickness, and forming a pattern by dry etching by a sand blast method while masking a part where a pattern is to be formed with photo resist, removing the resist, and forming a partition by burning (so-called sand blast method, see Patent document 2, for example).
In the thick film printing method, however, the thickness that is obtainable by a single printing operation is as large as about dozen micrometers, and the printing operation should be repeated about ten times in order to achieve the height of not less than 100 μm which is required for a partition. This raised the problem of poor productivity due to difficulty in positional registration of superposing printing and disability of obtaining height accuracy. Also in the sand blast method, since photo resist is used, the process is complicated because of necessity of exposure, development, removal of resist and the like steps, and it is difficult to form a partition with high accuracy because the lateral face of the partition is etched to be smaller than the width of the mask, or the bottom of the partition is widened.
For addressing this, a light-transmissive substrate having a certain pattern of a light shielding material formed on the surface, and a photoconductive material layer formed thereon is exposed to light from back side of the substrate, and developed after the light exposure. Next, using a model for a partition transfer intaglio having an appropriate pattern of projections on a substrate, an intaglio for transferring a partition is prepared, and then the recesses of the transferring intaglio are filled with a partition material to realize transferring to the substrate for a plasma display panel. A method of forming a partition of a plasma display panel including these steps is disclosed in Patent document 3. In this method, a resin containing glass powder is flown into a model in which a desired pattern of recesses are formed, a substrate is overlaid thereon, and then the model is removed by inversion to form projections formed of the resin containing glass powder on the substrate, by burning this, the glass component and the substrate are integrated to provide a partition (so-called transfer method). According to the transfer method, it is possible to provide a glass substrate having a partition more easily and conveniently than the sand blast method and the thick film printing method.
As a binder resin composition used for applications such as production of laminate ceramic capacitor, PDP and the like, for example, those based on ethyl cellulose, methyl cellulose, polyvinyl butyral, polyvinyl alcohol, polyethylene glycol and the like are considered and used. However, such binder resin compositions based on these resins have high thermal decomposition temperature, and when they are used for sintering low-melting temperature glass which is often used in PDP, for example, there arises the problem that decomposition residue of the binder resin is left in the sintered product.
For addressing this, a binder resin composition of low-temperature sintering type based on acrylic resin is examined. Patent document 4 discloses a methacrylic resin containing methacrylic acid alkyl ester component having a weight-average molecular weight of more than 200,000 and a glass transition temperature of −20 to 60° C. This methacrylic resin has low thermal decomposition temperature and is likely to be degreased during burning. Further, when a mixture containing ceramic powder is formed into a tape-like ceramic green sheet, excellent tape strength is achieved. However, the large molecular weight will cause so-called “stringiness” which is the phenomenon that the paste hangs from the printing plate like a string when it is used as a conductive paste and printed by screen printing.
Patent document 5 discloses a ceramic green sheet using an acrylic resin having an average molecular weight of 200,000 or more, an acid number of 2.4 to 7.2, and a glass transition temperature of 50 to 90° C. However, such acrylic resin sometimes causes “stringiness” when it is applied as a conductive paste and subjected to printing by screen printing or the like.
Patent document 6 discloses an acrylic resin composition containing as a binder component, an acrylic acid resin which comprises alkyl(meth)acrylate, unsaturated carboxylic acid, hydroxyl group-containing (meth)acrylate, and other copolymerizing monomers. This acrylic resin composition little causes “stringiness” because it causes the phenomenon called “stringiness cut” in which the paste does not hang from the printing plate in the form of string during printing by screen printing, and hence is tolerant to burning at low temperature. Although burning at lower temperature compared to conventionally used ethyl cellulose, polyvinyl butyral and the like is enabled, the burning temperature suited for degreasing is still as high as 450° C. This makes it difficult to realize satisfactory degreasing in the burning condition in which burning temperature is lower than that currently targeted, and sometimes leave residues at the time of burning.
Patent document 7, Patent document 8, Patent document 9, Patent document 10, and Patent documents 14 and 15 disclose resin binders having photoconductivity comprising (meth) acrylic polymer containing a repeating unit derived from (meth)acrylate monomer having a polyoxyethylene chain as a side chain and a hydroxyl group or an alkoxy group at an end of the side chain, used together with metal powder, fluorescent material, glass powder and the like.
Patent document 11 discloses a resin binder having photopolymerization ability which is a (meth)acrylic polymer containing a repeating unit derived from metacrylate monomer having a polyoxyethylene chain as a side chain and a carboxyl chain at its end, used together with metal powder, glass powder, ceramic powder and the like.
However, the (meth)acrylic polymer containing a polyoxyethylene chain as a side chain has a high water absorption rate and may absorb moisture under a high humidity environment. The moisture absorbed paste is problematic in that the sheet thickness is likely to vary when the paste is dried after applied by printing in a sheet form. Further, the burning temperature suited for degreasing is reported as 450° C. which is still undesired high burning temperature.
Patent document 12 discloses a material having photo-polymerizing ability containing as a multi-functional polymerizable monomer component, multi-functional (meth)acrylate having a polyoxyethylene chain as a main chain, used together with inorganic powder for forming insulators, dielectrics, resistors, conductors and the like inorganic structures. This material is used as a material for forming a resin binder.
Patent document 13 discloses a material having anaerobic polymerizing ability containing as a multifunctional polymerizing monomer component, a multifunctional (meth)acrylate having a polyoxyalkylene chain as a main chain such as hexaethylene glycol diacrylate or tetraethylene glycol dimethacrylate, used together with ceramic powder. This material is used as a material for forming a resin binder.
Patent documents 12 to 15 disclose resin binders which are (meth)acrylate polymers containing a polyoxyethylene chain as a main chain or a side chain.
In an acrylic resin binder containing a polyoxyethylene chain as a main chain, however, the resin binder is likely to absorb moisture because of the presence of the polyoxyethylene chain, and when the paste absorbs moisture in a high humidity environment, the viscosity of paste is difficult to be stabilized. Further, the burning temperature suited for degreasing is reported as 450° C. which is still undesired high burning temperature.
Patent document 1: JP-A 58-150248
Patent document 2: JP-A 5-182592
Patent document 3: JP-A 2000-11865
Patent document 4: JP-A 2004-59358
Patent document 5: JP-A 9-142941
Patent document 6: JP-A 2001-49070
Patent document 7: JP-A 9-132692
Patent document 8: JP-A 9-194548
Patent document 9: JP-A 9-194551
Patent document 10: JP-A 9-208640
Patent document 11: JP-A 2000-290314
Patent document 12: JP-A 11-316456
Patent document 13: JP-A 5-157035
Patent document 14: JP-A 9-315719
Patent document 15: JP-A 2004-142964